Simon, I love that you found that Aprilia Cabrio connection (and corrected the idea it was an Ardea). Thank goodness for the WWW-enabled communities we can all take advantage of.
Geoff, did you have any luck with your request to the Ardea group?
I'm about to post there with a request for a camshaft and set of cam followers. My S4's are both knackered, mutually knackered you might say as they have been in a sustained argument at the contact point! And I think they were misassembled in the past as were quite a few other assemblies on the car as I'm finding as I work through it.